Valves are used in order to control the flow of medium in a pipeline. Virtually all designs of valves (ball valve, poppet valve, slide valve, diaphragm valve, butterfly valve) have the property of the actuating forces of the closing member becoming larger with increasing pressure within the pipeline. At the latest in the shut-off state of the valves, the higher pressure differential often provides, at least proportionally, for increasing actuating forces or actuating moments. Explained by way of example of a poppet valve, this means that in the case of a closed valve the forces, which are required to raise the ball from the seat, increase approximately linearly with the increasing pressure differential. These forces can be very easily determined by taking the area of the seated cone times the pressure differential. Very similar conditions also prevail in the different known fitting designs such as ball valves, slide valves etc. This dependency of the closing forces is, in particular significant when such a valve is to be operated in a directly-controlled magnetic manner. At the latest in the case of seat diameters or cone diameters of 20 mm and greater and differential pressures of 40 bar and greater, the forces become so great that actuation of the poppet valve is possible by means of an electromagnet only with extremely high output. This is generally not acceptable and thus only few directly-controlled globe valves are found above DN25 and above PN25.
Nonetheless, in many cases electro-magnetically directly-controlled valves are required, for example in cases of use where no pressurised air or no hydraulics are available. An electrical power supply is nowadays available on virtually every machine or installation and thus electrically actuated solenoid valves always have their advantages.